Cationic Cure Kinetics of a Polyoxometalate Loaded Epoxy Nanocomposite

In this paper, results of the cure reaction kinetics and mechanical properties of phosphotungstate (PTA) loaded epoxy nanocomposites are presented.  PTA is a 1 nm size particle composed of a tungsten oxide shell and a phosphate group at the core and is part of a class of metal oxides called polyoxometalates.  PTA is dispersed in the epoxy resin up to volume fractions of 0.1.  Differential scanning calorimetry measurements show the cure of the epoxy resin to be sensitive to the concentration of PTA.  A kinetics study of the cure exotherm suggests that PTA acts as a catalyst promoting cationic homopolymerization of the epoxy resin.   A cure mechanism based on cationic propagation and termination reactions is proposed.  The cure kinetics are discussed in light of the activated chain end (ACE) and activated monomer (AM) cure reaction pathways.  High resolution TEM of the cured epoxy nanocomposite show the PTA to be well dispersed in the epoxy matrix.  Thermal mechanical and dynamic mechanical temperature sweep measurements show a reduction in the glass transition temperature and coefficient of thermal expansion and an increase in modulus of the cured nanocomposite as the PTA loading is increased.